1. Field of the Invention
The present invention relates to a process for the addition reaction of hydroxyl-containing compounds with alkynes or allenes with formation of aldehydes and ketones or derivatives thereof in the form of enol ethers or acetals or ketals in the presence of an amorphous zinc silicate or cadmium silicate catalyst. The present invention furthermore relates to a novel process for the preparation of a zinc silicate or cadmium silicate and to the catalyst thus obtained.
2. Description of the Related Art
The addition reaction of hydroxyl-containing compounds with alkynes or allenes is carried out virtually without exception using homogeneously dissolved catalysts, for example with acids, bases and transition metal complexes (cf. Houben-Weyl, Methoden der organischen Chemie, Vol. 6/3, page 233, page 90, Vol. 5/2a, page 738, Vol. 6/1d, page 136 and Vol. 7/a, page 816).
The acid catalysis is generally limited to the addition reaction with activated, electron-rich alkynes (such as acetylene ethers, R--C.tbd.C--OR', acetylene thioethers, R--C.tbd.C--SR', and acetylene amines, R--C.tbd.C--NR'.sub.2).
Under base catalysis (in the presence of KOH or alcoholate) alcohols can be subjected to an addition reaction in the liquid phase also with inactivated alkynes. This is the most common method; however, the reaction requires high temperatures and pressures and the space-time yield is relatively low. Typically, a residence time of from 6 to 10 hours at about 160.degree. C. and from 18 to 20 bar are required for the base-catalyzed vinylation of an alcohol.
The addition reaction can also be catalyzed by transition metal complexes in the liquid phase. In particular, mercury(II) or gold(I) salts are suitable for the addition reaction of alcohols, while zinc and cadmium salts are preferred for the addition reaction of carboxylic acids and phenols.
The addition reaction of carboxylic acids (in particular acetic acid and propionic acid) with acetylene can also be carried out in the gas phase in the presence of, as catalysts, corresponding zinc carboxylates (including basic zinc carboxylates according to CH 239 752) on carriers having a large surface area.
Finally, the addition reaction of methanol with propyne or propadiene in the gas phase in the presence of zinc oxide on activated carbon or silica gel has also been described in DD 265 289 and that in the presence of zinc nitrate on activated carbon or silica gel in DD 267 629 at above 200.degree. C.
All these prior art processes have disadvantages. They either have only limited application or, like the base-catalyzed addition reaction, require high pressures and temperatures, which may lead to safety problems, or they have only a low space-time yield. Homogeneously dissolved transition metal catalysts are often deactivated after a small number of cycles and in addition are difficult to recycle. Heterogeneous catalysts for the addition reaction with alkynes or allenes have only rarely been described to date. Zinc carboxylates or cadmium carboxylates on activated carbon catalyze only the addition reaction of carboxylic acids (eg. acetic acid or propionic acid) with acetylene. The abovementioned catalyst based on zinc oxide on activated carbon or silica gel (DD 265 289) is capable of catalyzing the addition reaction of alcohols (methanol or ethanol) with propyne or propadiene with good selectivity (from 90 to 96%), but the catalytic activity is relatively low, the required reaction temperatures are high and the necessary contact times are long, leading to rapid deactivation of the catalyst. Even at the temperature of above 200.degree. C. used in DD 267 629, zinc nitrate on activated carbon or silica gel is about an order of magnitude less active than zinc oxide and the selectivity is much lower (max. 70%).